Abstract: The grating displacement transducer and the piezoelectric crystal pressure transducer are used to construct the electrodes displacement and the dynamic electrodes force quality control system in spot welding .The control theory , characteristic and effect are analysed and compared. The experimental result shows that the spot welding quality can be controlled by this sort of single parameter quality control system.The control systems have the self adaption characteristic ,and can be applied to construct multi parameters quality control system in spot welding.